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“SPEED, SPEED, SPEED” Warning

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“SPEED, SPEED, SPEED” Warning

Old 21st Feb 2018, 16:17
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Doesn't the autothrust not reengage below 100' so you end up getting climb thrust and doing a fly by?
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Old 22nd Feb 2018, 02:09
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Originally Posted by Checkboard
An aural low-energy “SPEED SPEED SPEED” alert, repeated every 5 s, warns the pilot that the aircraft’s energy level is going below a threshold under which he has to increase thrust, in order to regain a positive flight path angle through pitch control.
Thanks. As I suspected, it's not just speed but total energy. In this case, then, the proper warning should be "ENERGY." Or "POWER," which is the rate of change of energy; but as some have pointed out, that might be confused with the engine instruments. So my vote is for "ENERGY."

As most of us agree, the warning should point to the paramater in error. But despite your quote and others' elucidations, many still seem to point to the airspeed as the errant parameter, while from my understanding the speed can be perfectly normal and you can still get the warning.

Originally Posted by _Phoenix
By definition Speed, speed, speed is a warning about the low state of energy, about decaying of the kinetic energy, which is 1/2*m*speed^2. The flight instructor would warn the student in the same way about dangerously low speed condition, thenafter the student realizes that he has to add more power or to relax the pitch up (in a tight turn for instance).
Not so. Speed is kinetic energy, not "energy." "Energy" is total energy, which is specifically what this warning references. For more detail, I'll just quote my own post from the high altitude stall thread.:


On a serious note, a big pet peeve of mine about this topic is when people call it a "high altitude, low energy" situation. It is not low energy, from 30,000 feet you have gobs of energy below you (namely, 1491 knots' worth) to use. That is, as long as you have the understanding and fortitude to use it.

Of course, I know they mean "low kinetic energy" and not "low total energy," but in that case they could have just said "low airspeed" with no loss of information. But no, they have to muddy the waters by using the fancy high tech sounding term. Unqualified "energy" is supposed to mean "total energy."
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Old 22nd Feb 2018, 02:29
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Originally Posted by Checkboard
If you are at F speed and make a 90º turn onto final then a very small overbank will have you into the "SPEED SPEED" regime. The aircraft isn't smart enough to look ahead at the flight path and see that you will be manoeuvring - that's what pilots are for. Blind reliance on the managed speed "keeping you safe" gets pilots into trouble. I would imagine that the poster who has seen this "three times in seven years" was also relying totally on managed speed.
I also said "you'd be foolish to be anywhere near VLS unless you're flying in a straight line even on a nice day", suggesting that being anywhere near final app speed was a bad move unless you're actually about to land...
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Old 22nd Feb 2018, 03:15
  #24 (permalink)  
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Originally Posted by vilas
My guess is it can be seen it's a warning for approach and landing configurations. Airbus design philosophy is to use available automation. So with ATHR available it's not a thrust issue as thrust would already be at CLB. So it is change of flight path to get the correct speed. Taking thrust levers out of CLB for more thrust has been stopped by Airbus.
Vilas,

Can you quote something from the FCOM on that, our manual specifically directs to advance thrust.
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Old 22nd Feb 2018, 04:04
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As Vessbot stated well, it is total energy state, I have been at 45,000’, pointed straight up, with 0 airspeed in an F-16, the least of my worries at that time was the airspeed my aircraft.

Three speed warnings. Two which I believed to be either spurious or extraordinarily conservative (that statement will certainly aggravate some, but after 36 years of flying, I believe I have a pretty good understanding of the energy state of my aircraft - I have not and would never maneuver a commercial aircraft aggressively)

All that said, the time I believed the warning which was valid was what I described and my FO’s instinctive reaction to it, which was inappropriate. His response was to add 10 knots to the SEL speed, because the airplane announced, “Speed, speed, speed.”. The warning is based on the current energy state and the FAC’s expected energy state of the aircraft. His reaction was incorrect.

Airbus designed this to focus the pilots attention on the energy state of the aircraft, yet the callout was speed thus my OP.
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Old 22nd Feb 2018, 04:11
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What was the vertical mode, was the airplane pitching to maintain speed?
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Old 22nd Feb 2018, 04:59
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CaptainMongo
Can you quote something from the FCOM on that, our manual specifically directs to advance thrust.
This was in FCOM Bulletins but these days either they have disappeared or are impossible to find. Let me try another time.
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Old 22nd Feb 2018, 07:05
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tom775257
I suspect Vilas is referring to phase advance which used to be allowed, moving the thrust levers above the climb gate for a short period of time to temporarily get man thrust / MCT until you click it back into climb when Athr will reengage.
Yes! That's what I remember it was for approach. But it seems to have disappeared. What you find in FCTM is in connection with adverse weather.
WARNING THE FLIGHT CREW
The "SPEED, SPEED, SPEED" low energy warning (if available) is based on the aircraft speed, acceleration and flight path angle. This warning attracts the PF eyes to the speed scale, and request rapid thrust adjustment. In windshear conditions, it is the first warning to appear, before the activation of the alpha floor.
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Old 22nd Feb 2018, 08:01
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Of course, I know they mean "low kinetic energy" and not "low total energy," but in that case they could have just said "low airspeed" with no loss of information. But no, they have to muddy the waters by using the fancy high tech sounding term. Unqualified "energy" is supposed to mean "total energy
Actually they are correct, the total energy decreases under the work of the increased drag, since the initial total energy+work of drag force(-)=final total energy(lower). They say you have to increase Power(thrust force) to recover the lost of kinetic energy(and to recover the initial total energy) in order to keep the flight path. Otherwise, by keeping the lower total energy state you have to trade your potential energy towards the kinetic energy, before the alfa floor kicks in.
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Old 22nd Feb 2018, 08:50
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Mongo
Phew! Finally I got it. It's very long one.
REASON FOR ISSUE
During the approach, with the A/THR active, Airbus recommended to set the thrust levers above the CL detent (but below the MCT detent), in exceptional circumstances, if the speed significantly dropped below VAPP. However this procedure is not trained and proved to have more drawbacks than advantages. Therefore, Airbus no longer recommends to use this procedure. The procedure is deleted from the operational documentation.
If the A/THR performance is not satisfactory, the flight crew should take over, and control the thrust manually.
GENERAL
The purpose of this FCOM Bulletin is to highlight certain aspects of aircraft handling during final approach, and to illustrate that the feedback received from in-service experience merits further attention. Although approach in turbulence is part of this discussion, windshear in approach is not addressed
here. For more details on the subjects of "Windshear in Approach" and "Operations in Windshear or Downburst Conditions", Refer to PRO-SUP-91-20.
APPROACH STABILIZATION CRITERIA
The prerequisite for a successful final approach and landing is to stabilize the aircraft on the final approach trajectory in pitch, thrust, airspeed, and bank angle. This signifies that the:
‐ Aircraft is established on the:
• Final approach trajectory, and only minor heading corrections are necessary (except for indirect or curve approaches) to correct the effect of external conditions, acting on the roll axis
• Final approach vertical flight path, and only minor pitch corrections are necessary to correct the effect of external conditions;
‐ The target speed is maintained on the desired descent path, with the appropriate thrust (not stabilized at idle).
Airbus policy requires that stabilized conditions be reached at 1 000 ft Height Above Threshold in IMC, and 500 ft feet in VMC, and that they be kept down to the flare height.
In turbulent conditions, there may be heading, pitch, and thrust corrections of such a magnitude that it could be difficult to determine when to consider the approach stabilization criteria as being lost. Thrust corrections, in particular with the A/THR ON, could lead engines to temporarily reduce thrust to idle, which may not be desirable close to the ground, if the aircraft level of energy is low.
A318/A319/A320/A321 FLIGHT CREW
OPERATING MANUAL
FLIGHT CREW BULLETINS
AIRCRAFT HANDLING IN FINAL APPROACH
AXM A318/

Last edited by vilas; 26th Feb 2018 at 03:12.
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Old 22nd Feb 2018, 10:26
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“Speed, speed, speed.”. The warning is based on the current energy state and the FAC’s expected energy state of the aircraft. His reaction was incorrect.
Airbus designed this to focus the pilots attention on the energy state of the aircraft, yet the callout was speed thus my OP.


Could it be that Airbus have tried to be overly smart and over simplify the a/c so that dummies can fly it,, but then they are caught out by the unexpected thinking pilot.
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Old 22nd Feb 2018, 11:59
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I heard that warning only once when my batch mate was doing his base flight and pitch up a bit too violently to lower the ROD during base leg and thus triggered the warning. From what I understand , in that case the warning can be stopped by either lowering the nose to recover a positive flight path angle and most likely an increase in airspeed or adding power which will also increase the speed. I don't see any situation where increasing the speed won't solve the problem. Therefore the Auto Call Out " Speed Speed Speed" does make sense to me.
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Old 22nd Feb 2018, 21:58
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Originally Posted by _Phoenix
Actually they are correct, the total energy decreases under the work of the increased drag, since the initial total energy+work of drag force(-)=final total energy(lower). They say you have to increase Power(thrust force) to recover the lost of kinetic energy(and to recover the initial total energy) in order to keep the flight path. Otherwise, by keeping the lower total energy state you have to trade your potential energy towards the kinetic energy, before the alfa floor kicks in.
I'm not sure exactly what you're addressing, but I'll take the blame since this time I muddled up the picture by posting an example from a different discussion. The underlying commonality is that people mistakenly call speed "energy" when they should be saying "kinetic energy."

In the high altitude example I posted, that leads them to mistakenly infer "low energy" from "low speed" and forget about all the potential energy below them.

The example that this thread is based on is someone inferring "low speed" from the warning that's about low energy (but you can't really blame him, since the plane said "SPEED!") and increasing the speed (presumably via pitching down; CaptainMongo didn't clarify but that's what I'm inferring) which only worsened the total energy loss.

Last edited by Vessbot; 23rd Feb 2018 at 02:34.
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Old 23rd Feb 2018, 03:41
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Vessbot,

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Old 23rd Feb 2018, 04:02
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Sorry, I'm not following. You'll have to be more specific with what you're replying to and how your facts bear on that.
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Old 23rd Feb 2018, 11:52
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It is about the conservation of the mechanical energy. The state of energy of a system can increase by receiving work = Force*distance or it can decrease by dissipating energy through friction (converted in thermal energy). In imagine at point A the total energy is U1 = beer_mass*g*h since vA = 0 . The the beer is accelerated by the total force (Fapp-Friction), that produces work (Fapp-Friction)*dAB. At point B the energy = U1 + K2 , where K2 = 0.5*beer_mass*vB^2. At point B the Fapp becomes =0 and only the Friction force change the energy state from K2 +U1 (at point B) to U1 at point C. The friction work=Friction*dBC = -K2.
Same logic at point C' the energy U2 = U1 + beer_mass*g*delta_h and the travel is shorter, part of the kinetic energy is changed into potential energy (the work of the gravity component acting on the same direction as the Friction force)
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Old 23rd Feb 2018, 14:21
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U is potential energy, not total. It's defined right there in the, um, definitions. Total is K+U. That's making the rest of your math jumbled. Also things with subscript 2 correspond with position C, not B. Also there are two separate scenarios; the first on the flat plane where potential energy stays the same, and the second up the incline where potential energy increases.

All that aside, you still didn't say what part of my post that bears on, or how it bears on it.
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Old 23rd Feb 2018, 15:14
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K=0 for v=0, I stated above for the feeling that I have to make it clear. There are two equations for energy conservation with K1=K3=0. Sorry, that's all, I'm at work, otherwise I would open a beer and listen to this hit: Echame La Culpa.
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Old 23rd Feb 2018, 17:41
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Airbus cadet pilots are transferring from 'Flying for Dummies' aeronautical college to MIT so they can understand WTF the a/c is talking about.
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Old 24th Feb 2018, 00:55
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It's a simple warning in approach about falling speed. Some thing like verbal trend arrow. Apart from WS the reason is flight path or thrust if in manual thrust. The practice of moving the thrust levers out of CLB towards MCT if taken too far has the potential(actually I am sure it has happened) of triggering GA mode which will effectively end the approach. So through the FC Bulletin which I mentioned it was stopped and complete switching to manual thrust was recommended. Either the the earlier or the later recommendation doesn't seem to exist in Airbus new manuals. So if a company manual has it then it will be a good idea to get Airbus position on the matter under tech request.
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